1. Field of the Invention
The present invention relates to a radio communication and data processing system for a vehicle and, in particular, to a road navigation system or an automatic drive guidance system for an automobile or the like.
2. Prior Art
FIG. 1 shows a block diagram of a conventional road navigation system as disclosed, for example, in Japanese Patent Public Disclosure (KOKAI) No. 57-206813 in 1983. In the drawing, numeral 1 denotes a display unit, numeral 2 denotes a CPU, numeral 3 denotes a location information unit, numeral 4 denotes a RAM, numeral 5 denotes an orientation sensor, numeral 6 denotes a velocity sensor, and numeral 7 denotes an output unit.
In operation, the display unit 1 visually displays a road map which a vehicle driver may wish to refer to. By means of the location information input unit 3, a screen marker is traced from a departure point to a destination point on the display unit 1, so that information on a course or route which it is intended to follow is stored in the RAM 4. Then, the marker is set at the departure point when the journey is started. During the journey, the current location of the vehicle at any one time can be computed by the CPU 2 in accordance with information provided by the orientation sensor 5 and the velocity sensor 6 and the marker on the display unit 1 is moved on this basis. Also, by means of the CPU 2, the computed current location information can be compared with the intended course or route information stored in the RAM 4 to determine whether the vehicle is exactly on course. If it is off course, an alarm indication, or a guidance message indicating, for example, which way the driver should turn at the next road crossing or intersection can be provided from the output unit 7 which may include a loudspeaker.
Since the conventional road navigation system is constituted in the manner described above, it is difficult to accurately obtain the current location information due to signal errors caused by the orientation sensor and the velocity sensor. Therefore, this system has shown a tendency to give wrong guidance or indications to the vehicle driver.